Technological development and increased demand for mobile instruments has lead to a rapid increase in the demand for secondary batteries as an energy source. Among these secondary batteries, a great deal of research and study has been focused on a lithium secondary battery having high energy density and discharge voltage and thus such lithium secondary batteries have been commercialized and entered wide use.
Recently, a great deal of attention has been directed to the lithium secondary battery using a Li—Si based active material as the anode. Pure silicon (Si) has theoretical specific capacity of 4200 mAh/g that is significantly greater than 372 mAh/g of graphite carbon. However, Si undergoes significant changes in volume thereof over continuous charge/discharge cycles, which causes mechanical and electrical degradation, and thus such poor charge/discharge cycle characteristics have been raised as the point at issue.
An attempt to solve such problems associated with charge/discharge cycle characteristics, some conventional arts have proposed a novel configuration of the electrode in which a surface of a copper current collector is made rough and an amorphous silicon film is vapor-deposited thereon. Such an electrode exhibits high reversible capacity of greater than 3000 mAh/g, but three still remains a need for further improvement of charge/discharge cycle characteristics thereof
The reason of capacity decrease occurring in the course of the charge/discharge cycle is generally known to be due to loss of electrical contact between the silicon film and current collector. Therefore, if a method for improving electrical contact between the silicon film and current collector in the lithium secondary battery made up of the Li—Si based anode could be developed, it will be possible to manufacture a lithium secondary battery having excellent charge/discharge cycle characteristics.